The Lower Tarim River in NW China is under severe ecosystem degradation due to stopped stream flow and diminished groundwater recharge. Since 2000, the water diversion project from the upper stream and from the neighboring Kaidu-Kongque River (cost US$ 1.6 billion) has been implemented to alleviate the ecosystem disaster. Up to now, a total volume of 2.3 billion m3 of water has been diverted to the lower reaches by nine water diversions, it’s still at the stage of compensation for groundwater recession. Sustainable water utilization and ecosystem protection scheme are imperative for the degraded ecosystem restoration and prevention of the Taklimakan Desert and the Kuluk Desert from merging in the Lower Tarim River. In order to increase the chance of success in riparian ecosystem restoration and to identify proper tracers of groundwater dynamics, it is important to gain knowledge of the hydrological and hydrogeochemical processes involved.
More recently, Prof. Zhonghe Pang from the Institute of Geology and Geophysics, Chinese Academy of Sciences and his Ph.D. student Tianming Huang sampled the riparian groundwater system in 2007 and 2008 along the 350 km-long river channel through the 40monitoring wells situated along nine transects perpendicular to the river and three soil profiles. Measurements on the samples have included environmental isotopes (18O, 2H, 3H) and water chemistry. The results show that remarkable changes have been induced by the water diversions. The observed response of riparian groundwater system includes general decrease in total dissolved solid (TDS) and rise of water table. Scope with greater than 1 m rise in water table is within ~700 m from the riverbank in the upper segments and ~300 m in the lower ones. Greater rise of water table occurs near the river bank. Tritium data show that the extent of modern recharge (since 1960), including that from the diverted water, is limited to 600 m from the riverbank at the upper segments and 200 m at the lower ones. Stable isotopes show that groundwaters, regardless of modern or pre-modern, are enriched in heavy isotopes and are plotted in parallel to the meteoric water line in the δ-δ plot, attributed to evaporation during recharge. Groundwater is generally of Na-Mg-Cl-SO4type and is formed by dissolution of minerals, such as halite, sulphate, and carbonates, based on component correlation matrices analysis. The salinity of groundwater is mainly affected by the salinity of the diverted water and of the local antecedent groundwater, salts in the unsaturated zone, evapotranspiration during recharge.
After the nine impulsive water diversions, the water tables have risen at differing degrees from the river bed and the composition, types, distribution and growth status of the riparian vegetation have changed correspondingly. However, the zone of small groundwater depth (less than 5 m) and scope (within 1000-1500 m to river bed) suitable for the most existing Populus euphratica and Tamarix ramosissima, the main species targeted by the rescue effort, restricts to 200 m from the riverbank, and narrows down towards downstream. The long-term stability of the ecosystem cannot be achieved by the current water diversion scheme and regulating/saving water in source-streams and the Upper/Middle Tarim River is crucial for continuing water diversion.
This study has recently been published by Journal of Hydrology （Huang and Pang. Changes in groundwater induced by water diversion in the Lower Tarim River, Xinjiang Uygur, NW China: Evidence from environmental isotopes and water chemistry. Journal of Hydrology, 2010, 387: 188-201 ）Download Here
